The present invention relates to electronic and electromagnetic circuits, and more particularly, to an apparatus for introducing an adjustable delay and phase shift onto an input signal.
In many electronic systems, it is necessary to adjust a phase and delay associated with a signal. Conventionally, the addition of delay to a signal is done using delay lines. For example, a series of delay lines is conventionally provided where each delay line has a fixed amount of delay. The delay lines may be connected together to provide discreet increases in delay.
Delay lines may be undesirable in applications that require a precise amount of delay because delay lines only add delay in discrete increments. Moreover, conventionally adjusting both delay and phase requires both delay lines and additional components for varying the phase. The additional components may need to be selected individually, for each manufactured circuit or system, depending on the particular manufacturing idiosyncrasies of the delay lines and the circuit or system itself.
In view of the shortcomings of conventional techniques, there is a need for an electrically adjustable circuit to precisely control delay and phase shift imparted to an input signal over a continuous, rather than a discrete, range of values. The need is particularly acute when the input signal is in the microwave range and precise delays in picosecond range are required.
According to the present invention, an apparatus provides an adjustable phase and time delay to an input signal. The apparatus includes an inverting element and first and second variable capacitors. The inverting element has a first end serially coupled with the input signal and a second end. The first variable capacitor is coupled between the first end of the inverting element and a first voltage. The second variable capacitor is coupled between the second end of the inverting element and a second voltage. The first and second variable capacitors are separately adjustable to controllably vary a phase shift and a delay of a reflection of the input signal. The reflection of the input signal is conveyed as the output signal. The first and second voltages may be at the same or a different potential, such as a ground potential or a ground or power potential of a power supply.
In one embodiment of the invention, the inverting element is a quarter wavelength transmission line. Either or both of the variable capacitors may be voltage variable, such as varactors, or they may be variable though manual adjustment. When the variable capacitors are voltage variable, a first adjustable voltage may be applied across the first variable capacitor and a second adjustable voltage may be applied across the second variable capacitor. The first and second adjustable voltages are separately adjustable, thus permitting separate adjustment of the capacitance values of the fist and second variable capacitors to controllably vary the phase and the delay of the reflected input signal.
The input signal may be coupled to the inverting element through a directional coupler, such as a circulator. The circulator has first, second and third ports and preferentially routes signals incident at one port to another port. For example, signals applied at the first port are routed to the second port and signals applied at the second port are routed to the third port. According to one embodiment of the present invention, the input signal is applied to the first port of the directional coupler and conveyed to the second port which is coupled with the first end of the inverting element. The input signal is reflected by the inverting element and variable capacitors back into the second port. The reflected signal is then output from the third port as an output signal having a desired phase shift and delay relative to the input signal.
A system for correcting the phase and delay of a linear amplifier according to the present invention includes a linear amplifier, a phase and delay shifting element, a coupler and an error circuit. The phase and delay shifting element is adjustable to impose a variable delay and phase shift to signals applied to its input. The coupler receives and divides an input signal into first and second signals and conveys the first signal to an input of the linear amplifier and the second signal to an input of the phase and delay shifting element. The error circuit is coupled to the outputs of the linear amplifier and the phase and delay shifting element and produces an error signal based on differences between the outputs.